Wheel suspension systems for two wheeled trailers have generally in the past limited the capacity of the trailers to the load capacity of the springs. It is well accepted that the actual trailer frame and body can be made strong enough to retain the weight. Similarly the wheel and axle can be made strong enough to support the load. The problem is vested with the capacity of the springing or suspension system of the wheels to the trailer frame. It has been common to use ordinary leaf springs arranged transverse to the axle and parallel to the trailer frame. Use has also been made of coil springs in lieu of the leaf springs with the coil springs mounted on the axle. It has also been known to mount the coil springs on stub axle for each wheel so that each wheel, in effect, is individually sprung and attached to the wheel frame. It has also been known to suspend the axle from an axle support frame which is pivotally attached to the trailer frame forward of the wheels with a coil spring arrangement at the rear. In this latter system the coil spring has been encased in a housing which is enclosed except for a slot in which the axle support arm on each side travels upwardly within the housing leaving an opening in the housing below the support arm which can collect soil, debris, and so forth when a load is placed on the trailer.
In these previous suspension systems the capacity of the trailer was dependent entirely upon the strength of the spring, that is, the heavier the load to be carried, the heavier the spring had to be in order to accept a load and at the same time provide some resiliency in the support system to compensate for irregularities in highways or in the ground over which the trailer was passing. Additionally, the previous systems generally did not include any means for restraining the up and down motion of the wheel in the event that a harmonic displacement of the wheels came about from the travel over the surface. Additionally, replacement of a broken spring was very difficult and required considerable equipment designed more or less to handle such disassembly.